Currently, the LED is used in the fields of illumination, display, backlight, etc., and attracts extensive attention due to its advantages such as energy saving, durability and being pollution free. There are many solutions for implementing the white LED, and presently the most mature technical solution for manufacturing the white LED is to implement white light emission by combining the blue light LED chip with the yellow fluorescent powder. Appl. Phys. Lett. published in 1967 (refer to volume 11, page 53) reports a light emitting material Y3Al5O12:Ce3+ which emits yellow light, with a maximum light emitting wavelength of 550 nm and a lifetime less than 100 ns. Appl. Phys. A published in 1997 (refer to volume 64, page 417) reports that white light emission of an LED is implemented using the yellow light emitted by Y3Al5O12:Ce3+ and blue light gallium nitride, which is the most mature technical solution for manufacturing the white LED at present. But in practical applications, with the increase of the temperature of the working device, the luminous intensities of the blue light LED chip and the fluorescent powder decrease, wherein the luminous intensity of the fluorescent powder decreases obviously, thus the usage of the LED is influenced.
The conventional LED is driven by the direct current (DC), but most of the household, industrial, commercial or public electricity is supplied in the form of AC, thus a rectifier transformer must be accompanied for AC-DC conversion when the LED is used for illumination, etc. But in the process of AC-DC conversion, a power loss up to 15˜30% will be caused. In addition, the conversion device has a short lifetime and a high cost, while it requires a lot of works and time in installation, so the efficiency is low.
The American patent U.S. Pat. No. 7,489,086 B2 “AC LIGHT EMITTING DIODE AND AC LED DRIVE METHODS AND APPARATUS” provides an AC LED device, which mainly enables an integrated packaged LED device to work in a frequency higher than 100 Hz, so as to compensate for the stroboflash of light emission of the LED device in the AC working state with a visual persistence effect of naked eyes. The Chinese patent No. 200910307357.3 discloses a light emitting material Y2O3•Al2O3•SiO2:Ce•B•Na•P with yellow long afterglow phenomenon and a white LED device using the same.
The Chinese patent CN100464111C discloses an AC LED lamp using LED chips of different emitting colors connected in parallel in an AC power supply, and it mainly describes different colors of LED chips used together for emitting white light, and the specific circuit thereof, such as red, green and blue light emitting chips. The international patent WO2004/023568A1 “LIGHT-EMITTING DEVICE HAVING LIGHT-EMITTING ELEMENTS” proposes to install a plurality of small LED chip arrays on a sapphire substrate, so as to provide a light emitting device that can be driven by an AC power supply. On the basis of similar ideas, the Seoul Semiconductor of South Korea and the Industrial Technology Research Institute of Taiwan integratedly package a lot of superfine LED grains onto a substrate referred to as AC LED chip. The core of the above AC LED technology is the microelectronic circuit processing technology integratedly packaging a lot of micro grains, e.g., the AC LED chip manufactured by the Industrial Technology Research Institute of Taiwan integratedly packages hundreds of tiny LEDs in an area of 1 mm2. But it is difficult to process the AC LED chip, and problems such as poor heat dissipation will be caused as the large number of microchips are integrated in a narrow substrate space.
In order to enable the white LED device to overcome the stroboflash under the AC power supply mode and improve the heat dissipation, persons skilled in the art always make unremitting efforts.